Subcritical Water Extraction Conditions Research Articles

Subcritical Water Extraction of Rosmarinic Acid from Lemon Balm (Melissa officinalis L.) and Its Effect on Plant Cell Wall Constituents.

Rosmarinic acid (RA), an ester of caffeic acid and 3,4-dihydroxyphenyllactic acid, is a potent radical scavenger, a chelator of prooxidant ions, and an inhibitor of lipid peroxidation. RA-containing extracts are widely used natural antioxidants in food products, and many herbal preparations and food supplements, containing RA, are marketed with claims of beneficial health effects. The current study investigated the effectiveness of subcritical water extraction (SWE) for the recovery of RA from lemon balm (Melissa officinalis), as a "green" alternative to conventional hydro-alcoholic extraction. Different durations (10 min and 20 min) and extraction temperatures (100 °C and 150 °C) were applied. Subcritical water applied at a temperature of 100 °C was equally efficient as 50% ethanol in extracting RA. However, the further elevation of temperature to 150 °C decreased RA content by up to 20% due to thermal degradation. The content of RA in dried extracts was between 2.36% and 5.55% and the higher temperature of SWE increased extract yield by up to 41%. The higher extraction yield resulted from the degradation of plant material by subcritical water as evidenced by the increased extraction and degradation of proteins, pectin, and cellulose. These results reveal that SWE is an efficient technology for the extraction of RA and other antioxidants from lemon balm at reduced extraction time and without the use of toxic organic solvents. Furthermore, by modification of SWE conditions, dry extracts with different purity and content of RA are obtained. These extracts could be used in the food industry as food antioxidants, or in the development of food supplements and functional foods.

Production of Rice-By Product Protein Isolate Using the Subcritical Water Extraction Method

Background: Subcritical water extraction (SWE) is a friendly technique applied to produce rice by-product extract. The aim of this study is using SWE as a new friendly extraction method for producing protein isolates (PI) of rice bran and rice combination as a byproduct of Iranian agriculture product. Methods: D-optimal combined design was used to optimize bran rice ratio, solid/water ratio, extraction time, and particle size to obtain maximum protein. Bran (8-12%) and rice ratio (88-92%) solid water (0.04 -0.12%), time (15-45 min), and particle sizes (420 µm and 710 µm) were selected as independent variables, and protein as dependent variable. After optimization, the effects of extraction parameters on functional properties were investigated. Results: Increasing bran/rice ratio has a significant effect on the protein extraction. In this study, the optimum SWE conditions were solid water (0.12), bran rice ratio (8:92), time (45 min), particle size (420 µm), and the optimum SWE temperature was obtained at 120 Cº. SWE also could significantly enhance functional properties, such as the solubility, emulsifying activity index (EAI), and degree of hydrolysis of by-product of rice milling (BRM) PI. Conclusion: According to the positive impact of SWE on protein extraction and the functional properties of BRM PI, this method could be applied as a novel extraction technique to modify the properties of rice protein isolate for functional purposes in the future. However, more investigation is required to study the quantity and quality of the extracted valuable materials to scale it up for industrial means.

Extraction of Phytochemicals from Maypole Apple by Subcritical Water.

The Maypole apple is a new, promising species of small apples with a prominent flavor and deep red flesh and peel. This study divided Maypole apples into outer flesh, inner flesh, and peel, and used subcritical water at 100-175 °C for 10-30 min to extract various phytochemicals (procyanidin B2 (PB2), 5-caffeoylquinic acid (5CQA), and epicatechin). The obtained Maypole apple extracts and extraction residues in this work were analyzed using a SEM, HPLC, FT-IR, and UV-Vis spectrophotometer. Under different subcritical water extraction conditions, this work found the highest extraction rate: to be PB2 from the peel (4.167 mg/mL), 5CQA (2.296 mg/mL) and epicatechin (1.044 mg/mL) from the inner flesh. In addition, this work regressed the quadratic equations of the specific yield through ANOVA and found that temperature is a more significant affecting factor than extraction time. This aspect of the study suggests that phytochemicals could be obtained from the Maypole apple using the new extraction method of subcritical water.

Study on the rice milling byproduct extracted by subcritical water extraction and its fermented milk analogs

The subcritical water extraction (SWE) method, as a proper alternative to conventional methods due to low cost, short processing time, environmental sustainability, and mild operating conditions, has been applied to produce valuable materials from different biomass. Rice milling byproduct (RMB) as abundant and locally available agricultural wastes is normally used for extracting oil and as animal feed. In this study, the quality and quantity of valuable compounds extracted by the SWE were investigated to select the optimum SWE conditions and the best extract to produce healthy cereal-based milk analogs. The most appropriate SWE parameters were investigated by the combined design method were 130°C and 45 min, rice bran: broken rice ratio of 10:90, the solid-water ratio of 0.12, and a particle size of <710 μm, respectively. SWE positively affected the release and production of some bioactive compounds such as total phenolic, flavonoids, organic acids. The milk analogs consisted of the optimum RMB extract, inulin, and Persian grape molasses (as a sucrose alternative) were then fermented by either Lactobacillus casei or Lactobacillus plantarum (0.5 McFarland). The fermentation process also rose the values of some nutrients, including vitamin B (B3, B6, and B9), organic acids, total phenolic compounds, and flavonoids. it decreased the contents of monosaccharides (p < .5), while the increased content of alcohol was negligible (<0.3%). Compared with L. plantarum, L. casei had a higher impact on the production of these bioactive compounds and more considerably increased antioxidant activity of the related beverages; nevertheless, beverages containing L. plantarum had the greatest over-acceptability. Moreover, the survival of L. casei and L. plantarum in beverages was in the standard range (106–108 CFU/ml) during storage, demonstrating that RMB ingredients along with inulin can positively affect LAB survival. Novelty impact statement The innovative aspect of this work is related to the use of Iranian agricultural byproduct such as BRM and Persian Grape Molasses in production of milk analogs containing Persian type culture collection and the use of subcritical water extraction as an environmentally friendly method for the production of functional beverages.

Comparison of Alliin Recovery from Allium sativum L. Using Soxhlet Extraction and Subcritical Water Extraction

Garlic (Allium sativum L.) is an herbaceous plant and is recognised for its numerous medicinal and culinary properties, and it is used in diverse food preparations for its characteristic flavour and aroma. High alliin content increases the formation of allicin, a bioactive compound of garlic. Therefore, this research aimed to compare different extraction methods for garlic (Allium sativum L.) between subcritical water extraction (SWE) and Soxhlet extraction to obtain a high extraction yield and alliin content. The SWE conditions were 120 °C and 180 °C temperatures and 2 mL/min and 6 mL/min flow rates at a constant pressure of 15 MPa for a 10 min extraction time, respectively. In the meanwhile, the extraction time for Soxhlet extraction with various solvents, namely, distilled water, ethanol–water (1:1), and 100% ethanol, was two hours. High-performance liquid chromatography (HPLC) was used to analyse alliin. Soxhlet extraction had the best yield (1.96 g) using ethanol–water (1:1) as the solvent in comparison to SWE extraction (1.28 g) at 180 °C and 6 mL/min. In contrast, SWE yielded a greater concentration of alliin (136.82 mg/g) at 120 °C and 2 mL/min than the Soxhlet method when using distilled water as the solvent (65.18 mg/g). Therefore, SWE may replace Soxhlet extraction as the conventional method for extracting alliin from garlic at a high concentration, and SWE has advantages that favour garlic extracts.

Extraction of monoterpenes from coriander (Coriandrum sativum L.) seeds using subcritical water extraction (SWE) technique

Subcritical water extraction (SWE) of monoterpenes from coriander seeds and effect of extraction conditions were investigated varying temperature (170–200 °C) and time (5–20 min). Monoterpenes was influenced by differences in their chemical structures and SWE conditions. The extraction efficiency of linalool was decreased with the increasing extraction temperature and extraction time, whereas linalool oxide was increased due to conversion of linalool to linalool oxide by hydrothermal oxidation. Geraniol, which has the same chemical formula as linalool, was extracted at a high temperature (170 °C) owing to the different placement of hydroxyl groups. The efficiency of SWE for geraniol (1.22 ± 0.22 mg/g) and linalool oxide (0.30 ± 0.09 mg/g) was higher than that of conventional extraction methods (hexane, methanol, hot water, and hydrodistillation). Therefore, SWE can be used to effectively and selectively extract monoterpenes by exploiting temperature changes in short extraction time.

Extraction of chlorogenic acids from hibiscus (Hibiscus syriacus L.) by subcritical-water

Chlorogenic acids are formed from hibiscus (Hibiscus syriacus L.) by ester bonding of caffeic acid and quinic acid, and they have isomers named neochlorogenic acid (NCGA) and cryptochlorogenic acid (CrCGA) that are esterified on different sites of caffeic acid. Subcritical-water extraction (SWE) is an ecofriendly and highly efficient technique because it utilizes a nontoxic solvent and has a very short extraction time. Twenty different SWE conditions were applied to hibiscus, with extraction times of 10–40 min, and extraction temperatures of 110–190 °C. The concentrations of chlorogenic acid, NCGA, and CrCGA were maximal for extraction conditions of 190 °C/10 min, 110 °C/10 min, and 130 °C/40 min, respectively. The extraction efficiency varied with the extraction conditions among the three isomers due to the hydrophilicity of the hydroxyl residue depending on the steric structure, the stability of the steric structure varying with the position of the acyl group, and the isomerization caused by the reversible movement of the acyl group.

Valorisation of microalga Tetradesmus obliquus grown in brewery wastewater using subcritical water extraction towards zero waste

In this study, green technology was applied for extraction of compounds from wastewater-grown microalga biomass with the final goal of obtaining microbiologically safe products within a sustainable biorefinery process with zero waste. Tetradesmus obliquus biomass resulting from brewery wastewater treatment, with (To-CO2) and without CO2 supplementation (To), was submitted to subcritical water extraction (SWE) at temperatures 120–220 °C for 10 min. The impact of the different SWE conditions in the obtained liquid extracts and solid residues were investigated for metal content and chemical and microbiological profiles. Gas chromatography–mass spectrometry analysis indicated that of T. obliquus extracts and residues are valuable sources of aliphatic saturated, unsaturated, and alkylated (mostly methylated) hydrocarbons, phenols, esters, and ketones. Polyphenolic content and antioxidant activity were enhanced approximately 4 times by increasing the temperature from 120 to 220 °C. Also, the content of polyphenols doubled when T. obliquus was supplemented with CO2 for all the tested temperatures (To: 0.249–1.016 mg GAE mL−1; To-CO2: 0.437 – 1.767 mg GAE mL−1). The microbiological analysis determined that liquid extracts and residues represent safe sources of bioactive components that can be used in different industries. In addition, the lower content of heavy metals in residues suggests the possibility of using the solid waste as animal feed or soil conditioner in agricultural applications.

Subcritical Water Extraction of Salvia miltiorrhiza

In this work, a green extraction technique, subcritical water extraction (SBWE), was employed to extract active pharmaceutical ingredients (APIs) from an important Chinese medicinal herb, Salvia miltiorrhiza (danshen), at various temperatures. The APIs included tanshinone I, tanshinone IIA, protocatechualdehyde, caffeic acid, and ferulic acid. Traditional herbal decoction (THD) of Salvia miltiorrhiza was also carried out for comparison purposes. Reproduction assay of herbal extracts obtained by both SBWE and THD were then conducted on Caenorhabditis elegans so that SBWE conditions could be optimized for the purpose of developing efficacious herbal medicine from Salvia miltiorrhiza. The extraction efficiency was mostly enhanced with increasing extraction temperature. The quantity of tanshinone I in the herbal extract obtained by SBWE at 150 °C was 370-fold higher than that achieved by THD extraction. Reproduction evaluation revealed that the worm reproduction rate decreased and the reproduction inhibition rate increased with elevated SBWE temperatures. Most importantly, the reproduction inhibition rate of the SBWE herbal extracts obtained at all four temperatures investigated was higher than that of traditional herbal decoction extracts. The results of this work show that there are several benefits of subcritical water extraction of medicinal herbs over other existing herbal medicine preparation techniques. Compared to THD, the thousand-year-old and yet still popular herbal preparation method used in herbal medicine, subcritical water extraction is conducted in a closed system where no loss of volatile active pharmaceutical ingredients occurs, although analyte degradation may happen at higher temperatures. Temperature optimization in SBWE makes it possible to be more efficient in extracting APIs from medicinal herbs than the THD method. Compared to other industrial processes of producing herbal medicine, subcritical water extraction eliminates toxic organic solvents. Thus, subcritical water extraction is not only environmentally friendly but also produces safer herbal medicine for patients.

A green strategy for obtaining anthraquinones from Rheum tanguticum by subcritical water

AbstractRheum tanguticum is a traditional Chinese herbal medicine, which contains abundant anthraquinones. In this study, anthraquinones were efficiently extracted from Rheum tanguticum by subcritical water extraction (SWE). The parameters of extraction time (33–67 min), temperature (100–200°C), and SW flow rate (1.4–4.6 mL/min) were optimized so as to achieve a high yield of the target product. A high yield of the total anthraquinones was achieved under the optimized SWE conditions of extraction time 54 min, extraction temperature 170°C, and the flow rate 2.0 mL/min. The comparison between the SWE and traditional extraction techniques implied that the SWE is an efficient and green alternative method for the extraction of anthraquinones. Four anthraquinone glycosides were purified from the SWE extract by high-speed counter-current chromatography and identified as emodin-1-O-β-D-glucoside, physcion-8-O-β-D-glucopyranoside, chrysophanol-1-O-β-D-glucoside, and chrysophanol-8-O-β-D-glucoside.

Facile and green preparation of diverse arabinoxylan hydrogels from wheat bran by combining subcritical water and enzymatic crosslinking

Feruloylated arabinoxylans demonstrate great potential in developing natural materials through oxidative crosslinking. However, the common alkaline method to extract arabinoxylans causes heavy losses of feruloyl esters thus hinders the crosslinking activity. Highly feruloylated arabinoxylans were fractionated from wheat bran by an alternative method using subcritical water extraction (SWE) and were compared with water- and alkali-extracted arabinoxylans. Various yields, chemical compositions, and molecular weights were obtained as the SWE conditions changed. Methylation analysis showed that the SWE arabinoxylans had a similar linkage pattern as the water-extracted arabinoxylan. Laccase-induced oxidative crosslinking was investigated through dynamic rheology, finding a broad spectrum of gelling ability for the SWE arabinoxylans. Finally, the optimal condition (160 °C, pH 7 for 10 min) was used in a repeated SWE procedure to maximize the yield and crosslinking properties. The combination of subcritical water and enzymatic crosslinking presents as a promising green approach for preparing hydrogels from herbaceous hemicelluloses.

Biochemical analysis and potential applications of aqueous and solid products generated from subcritical water extraction of microalgae Chlorella pyrenoidosa biomass

Subcritical water extraction (SWE) technology has become useful as a green extraction technology for generating various biochemical and bioactive compounds from a wide range of biomass feedstocks, including microalgae. SWE processes result in two different product phases: an aqueous phase containing solubilized or immiscible bioactive compounds from the extract, and solid-phase biomass debris containing residual or unextracted bioactive molecules in the matrix. While most SWEs of microalgal biomass focus on maximizing lipid production for biofuel application, the present work seeks to explore opportunities to identify and characterize compounds obtained from both the aqueous and solid phases. SWE of Chlorella pyrenoidosa biomass was carried out under varying conditions of temperature (170–370 °C), extraction time (1–20 min), and microalgal biomass loading (1–15%). Analysis of aqueous and solid-phase samples collected under varying SWE conditions showed a higher protein concentration of 4.13 mg mL−1 in the aqueous phase compared with carbohydrate (1.35 mg mL−1) for the optimum extraction conditions. About 17.52 mg g−1 of amino acids and 12.72 mg g−1 of organic acids were obtained from the aqueous phase with glutamic acid and lactic acid being the highest. The findings from this work would be useful in identifying and harnessing important microalgal biochemical from SWE process to develop new and improved bioproduct technologies.

Recovery of Antioxidant Compounds from Aronia Filter Tea Factory by -Product: Novel Versus Conventional Extraction Approaches.

Black chokeberry (Aronia melanocarpa L.) by-product from filter tea factory underwent subcritical water extraction (SWE) in order to recover polyphenolics and determine its antioxidant potential. In the current study Box-Behnken design was applied for optimization. Independent variables used in experimental design were temperature (T, 120-200 °C), extraction time (t, 15-35 min) and hydrochloride concentration (c, 0-1.5%). Experimental results were fitted to a second-order polynomial model where multiple regression analysis and analysis of variance were used to determine fitness of the model and optimal conditions. The optimized SWE conditions for maximum responses of total phenols (TP), total flavonoids (TF) and monomeric anthocyanins (MA) contents, and minimum response of IC50 were temperature of 120.4 °C, extraction time of 15.2 min and absence of acidifier. The predicted values of TP, TF, MA and IC50 at these conditions were: 32.8863 mg GAE/g, 23.5164 mg CE/g, 0.5124 mg C3G/g and 0.0055 mg/mL, respectively.

Optimization of Subcritical Water Extraction of Polysaccharides from Inonotus Obliquus and their Antioxidant Activities

Subcritical water extraction (SWE) of Inonotus Obliquus polysaccharides (IOP) was investigated using response surface methodology (RSM) with a design by Box–Behnken design (BBD). Results showed that the optimum SWE conditions for IOP production were as follows: extraction temperature 194°C, residence time 5.36 min and liquid-solid ratio 53 mL/g, yielding 168.80 ± 0.59 mg/g of IOP, which was in close agreement with the values predicted by the mathematical model. FT-IR spectra of the polysaccharides extracted by SWE and hot water extraction (HWE) were compared as well. Moreover, in vitro antioxidant assays revealed that SWE-IOP exhibited stronger scavenging activity that HWE-IOP. This investigation suggests that polysaccharides of Inonotus Obliquus extracted by SWE could be further developed as a potential antioxidant resource for dietary supplements of functional food.

Subcritical Water Extraction of Ursolic Acid from Hedyotis diffusa

An efficient and environmental-friendly extraction method has been developed for extraction of ursolic acid (UA) from Hedyotis diffusa by using subcritical water extraction (SWE). The experiments were carried out at different particle sizes (20–100 mesh), extraction temperature (120–200 °C), extraction time (10–50 min), solvent/solid ratio (20–40 mL/g), and extraction pressure (0.6–3.0 MPa). Response surface methodology (RSM) was employed to optimize SWE conditions, and the maximum UA yield was 6.45 mg/g material. Optimal conditions are as follows: Particle size of 80 mesh, extraction temperature at 157 °C and a solvent/solid ratio of 30 mL/g. The model of experimental response was proved to predict the experimental results very well and demonstrated that UA yield was mainly depended on solvent/solid ratio, followed by particle size and temperature. The purified extract was analyzed by electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). The acquired precursor ion was m/z 455.3532, which is consistent with calculated value of UA. Furthermore, different extraction methods, including maceration extraction, heat reflux extraction, ultrasonic extraction, microwave-assisted extraction, and SWE were comparatively analyzed, which indicated that SWE was a time-saving, cost-saving and environment-friendly extraction technology for extraction of UA from Hedyotis diffusa.

Recycling of filter tea industry by-products: Application of subcritical water extraction for recovery of bioactive compounds from A. uva-ursi herbal dust

In this study, classical extraction (CE) and subcritical water extraction (SWE) of polyphenolic compounds from A. uva-ursi herbal dust (a by-product of a filter tea factory) were performed. The extraction yields obtained through the application of these two extraction techniques were comparable, but higher a concentration of polyphenolic compounds (total phenols (TP) from 7.3088 to 10.6441g GAE/100g, and total flavonoids (TF) from 1.0344 to 1.8638g CE/100g) were recovered using SWE during a significantly shorter extraction time. SWE, as the more appropriate extraction technique, was further optimized by simultaneous maximization of total phenols (TP), total flavonoids (TF) yields and antioxidant activity. In order to optimize the SWE process, a Box-Behnken three level three variables experimental design was used. Temperature (T, 120–220°C), extraction time (t, 10–30min) and hydrochloride concentration (c, 0–1.5%) were independent variables. The experimentally obtained values were fitted to a second-order polynomial model. Multiple regression analysis and an analysis of variance (ANOVA) were used to determine model fitness and optimal conditions. The optimal SWE conditions were determined to be a temperature of 151.2°C, an extraction time of 10min and an addition of 1.5% HCl. The predicted values of targeted responses under these conditions were: 9.8431g GAE/100g, 1.7558g CE/100g, 5.02μg/ml and 27.60μg/ml for TP, TF, IC50 and EC50, respectively. Results suggested that A. uva-ursi herbal dust could potentially be utilized as raw material for the extraction of polyphenolic compounds, and that SWE instead of CE should be applied for this purpose.

Chemical characterization of polyphenols and volatile fraction of coriander (Coriandrum sativum L.) extracts obtained by subcritical water extraction

In this work, coriander (Coriandrum sativum L.) seeds were extracted by subcritical water extraction (SWE) at different temperature (100–200°C), pressure (30–90bar) and extraction time (10–30min), using Box-Behnken experimental design. Polyphenol compounds in obtained extracts were analyzed by HPLC–MS/MS, and 3,4-dimethoxycinnamic acid was dominant compound with the highest yield (942mg/100g DW) obtained at 100°C, 60bar and 10min. Chemical profile of volatile compounds was determined by GC–MS. Linalool, which is a dominant compound in coriander essential oil, was the most abundant volatile compound in all extracts obtained at 100 and 150°C, however, it almost completely degraded at 200°C. Total extraction yield (Y), polyphenols content (PC) and total volatile compounds (TVC) were response variables in investigated experimental design. Due to satisfactory statistical parameters, applied models for Y and PC represented good approximation of experimental results. Determined SWE conditions which provided maximized PC (1001mg/100g DW) were temperature of 100.5°C, pressure of 87.6bar and extraction time of 10min. Even though, TVC could not be optimized by RSM due to disagreement between observed results and second-order polynomial model, it is concluded that essential oil and polyphenol compounds could be co-extracted with a good yield at optimal conditions for PC, as the highest TVC was obtained at 100°C, 60bar and 10min.

Subcritical water extraction of sage (Salvia officinalis L.) by-products—Process optimization by response surface methodology

In this work, subcritical water extraction (SWE) of polyphenols from sage (Salvia officinalis L.) herbal dust was optimized by simultaneous maximization of total phenols (TP) and total flavonoids (TF) yields, as well as maximized antioxidant activity, determined by DPPH, ABTS and reducing power assay. Sage herbal dust, discarded as by-product from filter tea factory, was used as raw material for extraction. Three level, three variables, Box-Behnken experimental design (BBD) with response surface methodology (RSM) was used for optimization of SWE. Temperature (X1: 120–220°C), extraction time (X2: 10–30min) and HCl concentration in extraction solvent (X3: 0–1.5%) were investigated as independent variables. Experimentally obtained values were fitted to a second-order polynomial model, and multiple regression analysis and analysis of variance (ANOVA) were used to determine model fitness and optimal conditions. The optimal SWE conditions for simultaneous maximization of TP, TF and antioxidant activity were temperature of 201.5°C, extraction time of 15.8min and pure water as extraction solvent, while predicted values of TP, TF, IC50, TEAC and EC50 at this experimental point were 7.98g GAE/100g DW, 4.93g CE/100g DW, 13.38μg/mL, 38.34mM Trolox/100g DW and 41.66μg/mL, respectively. Results suggested that SWE provided significant advantages in terms of polyphenols yield, comparing to maceration, and that herbal dust from filter tea factory could be potentially utilized as good raw material for extraction of valuable bioactive compounds.

Optimization of subcritical water extraction of antioxidants from Coriandrum sativum seeds by response surface methodology

Subcritical water extraction (SWE) of antioxidants from Coriandrum sativum seeds (CSS) was optimized by simultaneous maximization of the total phenolics (TP) and total flavonoids (TF) yield and antioxidant activity, using IC50 value. Box–Behnken experimental design (BBD) on three levels and three variables was used for optimization together with response surface methodology (RSM). Influence of temperature (100–200°C), pressure (30–90bar) and extraction time (10–30min) on each response was investigated. Experimentally obtained values were fitted to a second-order polynomial model and multiple regression. Analysis of variance (ANOVA) was used to evaluate model fitness and determine optimal conditions. Moreover, three-dimensional surface plots were generated from employed mathematical model. The optimal SWE conditions obtained in simultaneous optimization were temperature of 200°C, pressure of 30bar and extraction time of 28.3min, while obtained values of TP and TF yields and IC50 value at this experimental point would be 2.5452g GAE/100g CSS, 0.6311g CE/100g CSS and 0.01372mg/ml, respectively. Moreover, good and moderate linear correlation was observed between antioxidant activity (IC50 value) and total phenolics content (R2=0.965), and total flavonoids content (R2=0.709) which indicated that these groups of compounds are responsible for antioxidant activity of C. sativum extracts.

Investigating the properties of subcritical water extraction with pharmaceutical tablets

The properties of subcritical water extraction (SWE) in the sample preparation of pharmaceutical tablets were investigated. Tablets comprised of microcrystalline cellulose excipients broke apart up to 80 times faster in subcritical water than they did in room temperature water, while those containing starch readily broke apart in either. Tablets containing starch were also observed to gelatinize or “paste” over several SWE conditions, impeding subsequent filtration and analysis. This effect was avoidable, however, since it was demonstrated to disappear with increases in extraction time and temperature or decreases in sample size. Using SWE, two common over-the-counter pharmaceuticals were extracted under optimized conditions from tablets comprised of either microcrystalline cellulose or starch excipients. Analyte recoveries of 95% or more were obtained at 150 °C for vitamin C (ascorbic acid) tablets in as little as 8 min for the extraction of a whole intact tablet, 6 min for two half tablets, and 5 min for a ground tablet. By comparison, this occurred at 250 °C in just 2 min for an intact slice of an acetaminophen tablet. Reproducibility was generally quite good with these trials producing RSD values of less than 2%. The results indicate that SWE can be a potentially viable and efficient method for the sample preparation of whole, sliced, or ground pharmaceutical tablets, and further exploration of this approach is promising.